U.S. patent number 8,133,838 [Application Number 12/558,757] was granted by the patent office on 2012-03-13 for water purification material.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Nobuyuki Ashikaga, Shinetsu Fujieda, Tatsuoki Kono, Shinji Murai, Akiko Suzuki, Hideyuki Tsuji, Katsuya Yamamoto.
United States Patent |
8,133,838 |
Tsuji , et al. |
March 13, 2012 |
Water purification material
Abstract
The present invention provides a water purification material
capable of selectively adsorbing phosphorus dissolved in
wastewater, and also provides a water purification method employing
the material. The water purification material comprises a composite
metal hydroxide containing iron ions and calcium ions in its
structure, and this composite metal hydroxide has a layered
structure. In the water purification method of the present
invention, the water purification material is brought into contact
with wastewater so as to remove and recover phosphate ions in the
wastewater.
Inventors: |
Tsuji; Hideyuki (Yokohama,
JP), Kono; Tatsuoki (Tokyo, JP), Suzuki;
Akiko (Tokyo, JP), Fujieda; Shinetsu (Kawasaki,
JP), Murai; Shinji (Sagamihara, JP),
Ashikaga; Nobuyuki (Kawasaki, JP), Yamamoto;
Katsuya (Kawasaki, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Tokyo, JP)
|
Family
ID: |
42036550 |
Appl.
No.: |
12/558,757 |
Filed: |
September 14, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100072140 A1 |
Mar 25, 2010 |
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Foreign Application Priority Data
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Sep 25, 2008 [JP] |
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2008-245198 |
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Current U.S.
Class: |
502/328;
502/406 |
Current CPC
Class: |
B01J
20/06 (20130101); C02F 1/288 (20130101); B01J
20/041 (20130101); B01J 20/0229 (20130101); C02F
1/281 (20130101); C02F 1/66 (20130101); C02F
2101/105 (20130101) |
Current International
Class: |
B01J
23/42 (20060101) |
Field of
Search: |
;502/300,328,400,406,439 |
Other References
Ookubo et al, Preparation of Phosphate Ion-Exchange Properties of a
Hydrotalcite-like Compound, Langmuir, 1993 pp. 1418-1422. cited by
other .
Kawamoto et al, Phosphorus Removal from Wastewater by Layer
Structure Inorganic Ion Exchanger with High Selectivity to
Phosphate Anion, 1999, pp. 875-881. cited by other.
|
Primary Examiner: Johnson; Edward
Attorney, Agent or Firm: Turocy & Watson, LLP
Claims
The invention claimed is:
1. A water purification material comprising a composite metal
hydroxide, wherein said composite metal hydroxide having a layered
structure containing iron ions and calcium ions; and said material
shows, as a result of X-ray crystal structure analysis, a
diffraction pattern in which a total intensity of the main peaks
attributed to calcium hydroxide or iron hydroxide is not larger
than 1/2 of an intensity of the main peak attributed to the layered
structure.
2. The material according to claim 1, wherein said composite metal
hydroxide has a hydrotalcite-like structure.
3. The material according to claim 1, wherein said composite metal
hydroxide is represented by:
[Ca.sup.2+.sub.1-xFe.sup.3+.sub.x(OH).sub.m] in which x and m are
numbers satisfying the conditions of 0.16.ltoreq.x.ltoreq.0.28 and
1.6<m<2.3, respectively.
4. The material according to claim 1, wherein said iron ions or
calcium ions are attached on the surfaces of composite metal
hydroxide layers constituting the structure of said composite metal
hydroxide.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from the prior Japanese Patent Application No. 2008-245198, filed
on Sep. 25, 2008; the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a water purification material
capable of selectively adsorbing dissolved components, such as
phosphate ions, contained in water such as river water, lake water,
marsh water, sewage and industrial wastewater.
2. Background Art
Recently, the rapid globalization of economic activities has
brought serious worldwide problems of water pollution and
environmental pollution. At the same time, production activities in
the global scale have led to exhaustion of resources and, as a
result, not a few elements are getting regarded as rare
elements.
Phosphorus is one of such rare elements. In these days, phosphorus
ore has been becoming scarce in the global scale. Accordingly,
phosphorus has been already considered as a rare element in recent
years. On the other hand, as one of the measures against
eutrophication problems of closed waters such as lakes, marshes and
bay waters, phosphorus emission standards are strictly regulated.
For removing phosphorus substances from the waters, it is widely
known that coagulants such as calcium compounds are added so as to
coagulate and precipitate the substances. However, since phosphates
in water are generally in the form of poorly sedimentary floating
matter, it is necessary to form floc so as to rapidly precipitate
the phosphates. Consequently, a great deal of sludge is
produced.
In order to treat the sludge in a large amount, it is inevitably
required to scale up the treatment facilities. Accordingly, this
costs a lot of money. Further, the coagulants make the floc contain
various kinds of ionic components, and it is costly to separate
them from the sludge. Because of these reasons, the sludge is very
often not reused but disposed of as industrial waste at great cost.
This is a problem.
As described above, in the case where phosphorus in water is
removed according to conventional methods, there are various
inefficient problems in the process of coagulation and
precipitation by adding calcium salts. For example, it takes a long
time to treat the phosphorus substances in water and moreover it is
necessary to scale up the facilities and to dispose of the
sludge.
In view of the above problems, a lot of new materials for water
purification have been proposed recently. For example, as for
removal of phosphorus substances, an adsorbent having a
hydrotalcite structure is proposed as a high performance phosphorus
remover (e.g., in Journal of Water and Environment vol. 22, No. 11,
875-881(1999), [in Japanese]). Hydrotalcite is a kind of layered
inorganic mineral compounds, and negative ions are contained among
the layers in the structure thereof. It is reported that, since the
negative ions among the layers are exchanged with phosphate ions in
water to remove them, the adsorbent can exhibit high phosphorus
removability.
However, even the hydrotalcite cannot selectively ion-exchange only
the phosphate ions in water. If carbonate ions or sulfate ions, for
example, are contained in the water, they are ion-exchanged prior
to the phosphate ions. This means that there is room for
improvement in the selectivity to phosphate ions.
From the conventional viewpoint, namely, from the viewpoint of only
the water pollution and environmental pollution, it is enough to
remove harmful components from water. However, in consideration of
the aforementioned problem of the fact that valuable resources are
getting exhausted in the global scale, it is very important in the
coming society to take into account the viewpoint of recovery and
reuse of the resources. Accordingly, it is very important for the
coagulants and adsorbents to be excellent in the selectivity as
well as in the abilities of coagulation and adsorption,
respectively. Particularly in regard to phosphorus, although a
large amount of substances thereof is contained not only in
household wastewater but also in industrial wastewater drained from
food factories, drug factories and the like, there is the serious
problem that phosphorus as a resource is becoming exhausted. It is,
therefore, desired to provide an adsorbent exhibiting such high
performance and selectivity as are not attained by conventional
adsorbents or coagulants.
Hitherto, there have been presented various proposals concerning
removers of water-dissolved components, particularly, of dissolved
phosphorus, which is nowadays a resource feared to be exhausted.
Most of the proposed removers are coagulants or adsorbents, but
they catch not only phosphorus but also many other elements and
hence have a problem of insufficient selectivity to phosphorus.
Since having poor selectivity to phosphorus, those coagulants or
adsorbents are to be disposed of as waste after they are used. This
is a serious problem from the viewpoint that phosphorus should be
efficiently recovered and reused. Further, it is another problem
that known coagulants form floc so as to promote precipitation of
the floating matter and consequently generate a large amount of
sludge.
SUMMARY OF THE INVENTION
The present invention in one aspect resides in a water purification
material comprising a composite metal hydroxide, wherein said
composite metal hydroxide having a layered structure containing
iron ions and calcium ions; and said material shows, as a result of
X-ray crystal structure analysis, a diffraction pattern in which a
total intensity of the main peaks attributed to calcium hydroxide
or iron hydroxide is not larger than 1/2 of an intensity of the
main peak attributed to the layered structure.
Also, the present invention in another aspect resides in a method
comprising a step in which the above water purification material is
brought into contact with wastewater so as to remove ionic species
in the wastewater.
Furthermore, the present invention in another aspect resides in a
method for purifying a wastewater containing phosphorus,
comprising:
preparing a water purification material comprising a composite
metal hydroxide having a layered structure containing iron ions and
calcium ions; and
selectively adsorbing the phosphorus contained in the wastewater by
contacting the water purigfication material with the
wastewater.
The present invention provides a water purification material
excellent both in phosphorus adsorbability and in phosphorus
selectivity. The water purification material according to the
present invention makes it possible to adsorb phosphate ions with
such high selectivity as is essentially impossible for known
coagulants or adsorbents to realize. Accordingly, it is enabled not
only to remove phosphorus from wastewater with high efficiency but
also to recover and reuse the removed phosphorus and, as a result,
to easily obtain phosphorus substances of high purity.
Further, even if the wastewater contains phosphorus in a high
concentration, the water purification material of the present
invention exhibits less lowered adsorbability as compared with
conventional water purification materials. The present invention,
therefore, provides a phosphorus adsorbent of very high
performance.
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention are described below.
The water purification material according to the present invention
comprises a composite metal hydroxide containing iron ions and
calcium ions. This composite metal hydroxide has a layered
structure in which plural layers are stacked. Each layer has a
basic structure in which octahedrons enclosing the calcium ions at
the centers are two-dimensionally arrayed. In the composite metal
hydroxide containing iron ions and calcium ions, the calcium ions
participating in the layers can be considered to be partly replaced
with the iron ions in the present invention. Accordingly, the
layers are positively charged as a whole. Since there are negative
ions and molecules of water of crystallization among the layers,
the composite metal hydroxide is electrically neutralized as a
whole.
The above structure of the composite metal hydroxide is similar to
that of hydrotalcite. The hydrotalcite is, for example, represented
by [Mg.sub.3Al(OH).sub.8]1/2CO.sub.3.sup.2-.2H.sub.2O. The
structure of hydrotalcite is essentially formed by stacked brucite
layers made of Mg(OH).sub.2. In each brucite layer, octahedrons
enclosing the magnesium ions at the centers are two-dimensionally
arrayed. The magnesium ions participating in the brucite layers are
partly replaced with the aluminum ions. Among the brucite layers,
there are carbonate ions and molecules of water of crystallization.
As for properties of the hydrotalcite having that structure, it is
known that the negative ions among the layers are exchanged with
other negative ions. Accordingly, the composite metal hydroxide
contained in the water purification material of the present
invention can be considered to have a hydrotalcite-like structure.
This means that the composite metal hydroxide used in the present
invention is by no means a simple mixture of iron hydroxide and
calcium hydroxide.
The composite metal hydroxide in the present invention contains
metal elements of calcium and iron, but may further contain other
metal elements (which are hereinafter referred to as "third
metals") unless departing from the scope of the present invention.
Examples of the third metals include magnesium, aluminum, zinc,
zirconium, lanthanum and cerium. If the third metals are contained
too much, they often affect the crystal structure and the like of
the composite metal hydroxide to impair the effect of the present
invention. How far the third metals affect the crystal structure of
composite metal hydroxide is dependent on the sizes and the like of
individual third metals, and therefore the third metals
individually have different allowable contents. In general,
however, the content of the third metal is preferably 5 mol % or
less, more preferably 5 mol % or less based on the total amount of
all the metal elements contained in the composite metal
hydroxide.
As described above, the composite metal hydroxide in the present
invention has a layered structure and contains negative ions among
the layers. There is no particular restriction on the negative
ions. However, since the composite metal hydroxide is used in the
water purification material, it is not preferred to release
unfavorable negative ions. It is, hence, preferred to contain
eco-friendly negative ions. Examples of the eco-friendly negative
ions include carbonate ions, halogen ions and sulfate ions.
The composite metal hydroxide in the present invention is presumed
to adsorb negative ions by the chemical action of the iron ions or
calcium ions with hydroxyl groups on the hydroxide surface.
Further, it is also considered that, since the composite metal
hydroxide has a layered structure, the negative ions can be not
only adsorbed on the surface but also caught and ion-exchanged
among the layers, whereby high removability can be obtained.
Phosphorus-containing ions among the negative ions, particularly,
phosphate ions are highly adsorbed on the composite metal hydroxide
in the present invention. Further, the composite metal hydroxide
can selectively adsorb phosphate ions. The adsorbability and
selectivity to phosphate ions are both so high as to be hardly
shown by other composite metal hydroxides such as known
hydrotalcite, and hence are specific characteristics of the
composite metal hydroxide in the present invention.
The iron ions and calcium ions are present on the surface of the
composite metal hydroxide according to the present invention. On
the other hand, a lot of hydroxyl groups are also present on the
surface of the hydroxide. The iron ions and calcium ions,
therefore, react with the hydroxyl groups and consequently are
attached on the surface, so that the resultant surface often seems
to be covered with iron hydroxide or calcium hydroxide. This means
that the water purification material of the present invention can
further contain iron hydroxide or calcium hydroxide as well as the
above composite metal hydroxide. Accordingly, in a diffraction
pattern of X-ray crystal structure analysis, the peaks attributed
to calcium hydroxide or iron hydroxide are often observed. If these
peaks are too large, namely, if the iron ions or calcium ions are
present on the surface in a too large amount, iron phosphate or
calcium phosphate are formed, respectively, when phosphate ions are
adsorbed, for example. Since the iron phosphate or calcium
phosphate is in the form of floating matter, the sedimentation
properties are seriously degraded in that case. Accordingly, the
iron ions or calcium ions on the surface of the composite metal
hydroxide is preferably in a small amount. The amount of iron ions
or calcium ions can be determined by X-ray crystal structure
analysis. In the diffraction pattern of X-ray crystal structure
analysis, it is necessary that the total intensity of the main
peaks attributed to iron hydroxide or calcium hydroxide on the
surface be not larger than 1/2 of the intensity of the main peak
attributed to the layered structure. As long as the amount of iron
ions or calcium ions is within the range satisfying the above
condition, the effects of ion-exchange among the layers and of
adsorption on the surface are sufficiently obtained without
impairing the sedimentation properties of water purification
material having adsorbed the dissolved ions.
The composite metal hydroxide preferably used in the present
invention is, for example, represented by the formula:
[Ca.sup.2+.sub.1-xFe.sup.3+.sub.x(OH).sub.2]. On the other hand,
normal hydrotalcite has a layered structure represented by
[M.sup.2+.sub.1-yM.sup.3+.sub.y(OH).sub.2][A.sup.p-.sub.y/p.qH.sub.2O],
and hence the metal hydroxide included in the water purification
material of the present invention can be considered to have a
structure similar to that. In the present invention, however, not
all the Ca and Fe ions participate in the fundamental structure of
hydrotalcite. It is one of the characteristics of the present
invention that Ca and Fe in the form of ions are attached on the
surfaces of brucite layers in the hydrotalcite structure.
Accordingly, to be exact, the stoichiometric ratio of the composite
metal hydroxide in the present invention is different from that
represented by the formula of hydrotalcite. However, it is another
characteristic of the metal hydroxide in the present invention to
have a layered structure characterizing the hydrotalcite structure.
The composition of the composite metal hydroxide in the present
invention, therefore, can be represented at least by the formula:
[Ca.sup.2+.sub.1-xFe.sup.3+.sub.x(OH).sub.m]. If the composite
metal hydroxide has the same structure as normal hydrotalcite, the
m in the above formula satisfies the condition of m=2. Actually, in
the present invention, the Ca and Fe ions are additionally present
on the surfaces of brucite layers and are liable to react with
hydroxyl groups in water. The m in the above formula, therefore, is
presumed to satisfy the condition of 1.6<m<2.3, which is
preferred in the present invention.
In the present invention, since it is indispensable to contain both
iron ions and calcium ions, the x in the above formula may satisfy
the condition of 0<x<1. However, in order to enhance the
effect of the invention, the condition is preferably
0.16.ltoreq.x.ltoreq.0.28, more preferably
0.2.ltoreq.x.ltoreq.0.25.
The composite metal hydroxide described above can be synthesized by
any method. For example, the kinds and amounts of metal compounds
as the starting materials are properly determined by reference to
the well-known preparation process for hydrotalcite, and thereby
the composite metal hydroxide can be desirably prepared from
them.
In a concrete example, the composite metal hydroxide can be
obtained from a hydrothermal reaction of a calcium-containing
compound with an iron-containing compound. There is no particular
restriction on the material compounds, and examples thereof include
chlorides, carbonates, nitrates and sulfates of calcium and iron.
The reaction solution preferably has a pH value in an alkaline
range. The reaction can be conducted under high pressure in an
autoclave as well as under atmospheric pressure. The reaction
conditions are selected depending on the structure, particle size
and the like of the aimed composite metal hydroxide. However, the
reaction temperature is generally 25 to 200.degree. C., preferably
60 to 95.degree. C., and the reaction pressure may be atmospheric
pressure. The reaction can be performed under high pressure or
reduced pressure in an autoclave. In that case, the pressure is,
for example, in the range of 0.01 to 2.0 MPa.
As described above, the water purification material of the present
invention comprises the above composite metal hydroxide. The
composite metal hydroxide can be directly used, for example, in the
form of powder. However, if necessary, it can be formed or molded
in various shapes according to the practical application. For
example, it can be granulated alone or with a binder, can be loaded
on an organic or inorganic film, or can be stuffed in a column.
Further, the preparation processes for known porous materials can
be applied. For example, when granulated with a binder, the
composite metal hydroxide may be fired after the binder is
impregnated therein, if necessary.
In the water purification method according to the present
invention, the aforementioned water purification material is
brought into contact with wastewater so as to remove ionic species
in the wastewater. There is no particular restriction on how the
water purification material is brought into contact with
wastewater. For example, the water purification material in the
form of powder or granulated particles is added into wastewater,
and stirred, if necessary, to adsorb negative ions, and then
precipitated out. This process is effective in treating a
relatively large amount of wastewater. Although it is feared that
the treatment facilities may need to be scaled up, the above
process has an advantage that a large amount of wastewater can be
treated in one batch. In a different way to bring the water
purification material into contact with wastewater, the wastewater
may be led onto a film supporting the water purification material
or into a column filled with the material. This process can be
carried out in relatively small treatment facilities, but the
amount of treatable wastewater is limited. Accordingly, it is
suitable for treating a small amount of wastewater.
The water purification method according to the present invention
can be applied to wastewater having any pH value. However, under
strongly acidic conditions, the water purification material is
feared to be dissolved. In view of that, the pH range where the
water purification method of the present invention is preferably
applied is in the range of pH 2.0 to 14.0, more preferably pH 3.0
to 13.0. Accordingly, when the method of the present invention is
used, the pH value of wastewater is preferably beforehand adjusted
so that the effect of the present invention can be fully
obtained.
Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects
is not limited to the specific details and representative
embodiments shown and described herein. Accordingly, various
modifications may be made without departing from the spirit or
scope of the general inventive concept as defined by the appended
claims and their equivalents.
EXAMPLES
The present invention is further explained by the following
examples.
Example 1
In pure water, 8.3 g of calcium chloride and 4.1 g of iron(III)
chloride were mixed. Aqueous NaOH solution was then added so that
the mixture might be alkaline, to obtain 200 mL of a solution. The
solution was kept at 80 to 100.degree. C. for a few hours, to
precipitate sediment. The sediment was collected by filtration,
washed, and dried at 90 to 100.degree. C. for a few hours to obtain
a sample 1. The sample 1 was a composite metal hydroxide of calcium
and iron. It was confirmed by ion chromatography and by ICP
emission spectroscopy that the sample 1 was a composite metal
hydroxide represented by: [Ca.sub.0.75Fe.sub.0.25(OH).sub.m]. It
was also confirmed by X-ray diffraction method that the above
composite metal hydroxide had a layered structure.
On the other hand, a mixed aqueous solution containing phosphate
ions, sulfate ions and nitrate ions, the concentrations of which
were each 20 mg/L, was prepared as a simulated wastewater. After 20
mg of the sample 1 was added into 50 ml of the simulated
wastewater, the mixture was stirred for 2 hours to undergo water
purification treatment. Thereafter, the supernatant solution was
collected and the concentrations of the ions contained therein were
quantitatively analyzed, to measure the amounts of residual ions
and adsorbed phosphorus. The results were as set forth in Table
1.
Example 2
The procedure of Example 1 was repeated except for employing 9.3 g
of calcium chloride and 2.6 g of iron(III) chloride as the starting
materials, to obtain a sample 2. It was confirmed in the same
manner as in Example 1 that the sample 2 was a composite metal
hydroxide represented by: [Ca.sub.0.84Fe.sub.0.16(OH).sub.m] and
that the above composite metal hydroxide had a layered
structure.
The water purification treatment in the same manner as in Example 1
was carried out by use of the sample 2. The results were as set
forth in Table 1.
Example 3
The procedure of Example 1 was repeated except for employing 7.6 g
of calcium chloride and 3.2 g of iron(III) chloride as the starting
materials, to obtain a sample 3. It was confirmed in the same
manner as in Example 1 that the sample 3 was a composite metal
hydroxide represented by: [Ca.sub.0.79Fe.sub.0.21(OH).sub.m] and
that the above composite metal hydroxide had a layered
structure.
The water purification treatment in the same manner as in Example 1
was carried out by use of the sample 3. The results were as set
forth in Table 1.
Example 4
The procedure of Example 1 was repeated except for employing 6.9 g
of calcium chloride and 4.1 g of iron(III) chloride as the starting
materials, to obtain a sample 4. It was confirmed in the same
manner as in Example 1 that the sample 4 was a composite metal
hydroxide represented by: [Ca.sub.0.72Fe.sub.0.28(OH).sub.m] and
that the above composite metal hydroxide had a layered
structure.
The water purification treatment in the same manner as in Example 1
was carried out by use of the sample 4. The results were as set
forth in Table 1.
Example 5
The procedure of Example 1 was repeated except for preparing the
simulated wastewater so that the concentrations of phosphate ions,
sulfate ions and nitrate ions might be each 40 mg/L, to perform the
water purification treatment. The results were as set forth in
Table 1.
Example 6
The procedure of Example 5 was repeated except for employing the
sample 2, to perform the water purification treatment. The results
were as set forth in Table 1.
Example 7
The procedure of Example 5 was repeated except for employing the
sample 3, to perform the water purification treatment. The results
were as set forth in Table 1.
Example 8
The procedure of Example 5 was repeated except for employing the
sample 4, to perform the water purification treatment. The results
were as set forth in Table 1.
Comparative Example 1
In pure water, 8.0 g of aluminum chloride and 1.9 g of magnesium
chloride were mixed. Aqueous NaOH solution was then added so that
the mixture might be alkaline, to obtain 200 mL of a solution. The
solution was kept at 80 to 100.degree. C. for a few hours, to
precipitate sediment. The sediment was collected by filtration,
washed, and dried at 90 to 100.degree. C. for a few hours to
prepare a sample 5. The sample 5 comprised a hydrotalcite
containing magnesium and aluminum. The water purification treatment
in the same manner as in Example 1 was carried out by use of the
sample 5. The results were as set forth in Table 1.
Comparative Example 2
The procedure of Example 5 was repeated except for employing the
sample 5, to perform the water purification treatment. The results
were as set forth in Table 1.
Comparative Example 3
The procedure of Example 1 was repeated except for employing 9.7 g
of calcium chloride and 2.1 g of iron(III) chloride as the starting
materials, to obtain a sample 6. It was confirmed in the same
manner as in Example 1 that the sample 6 was a composite metal
hydroxide represented by: [Ca.sub.0.87Fe.sub.0.13(OH).sub.2] and
that the above composite metal hydroxide had a layered structure.
However, in the X-ray diffraction pattern thereof, the intensity of
the peak attributed to calcium hydroxide was larger than 1/2 of the
intensity of the peak attributed to the layered structure. The
water purification treatment in the same manner as in Example 5 was
carried out by use of the sample 6. The results were as set forth
in Table 1.
Comparative Example 4
The procedure of Example 1 was repeated except for employing 7.7 g
of calcium chloride and 5.0 g of iron(III) chloride as the starting
materials, to obtain a sample 7. It was confirmed in the same
manner as in Example 1 that the sample 7 was a composite metal
hydroxide represented by: [Ca.sub.0.70Fe.sub.0.30(OH).sub.2].
However, it was found that a layered structure was not formed
essentially in the above composite metal hydroxide. The water
purification treatment in the same manner as in Example 5 was
carried by use of the sample 7. The results were as set forth in
Table 1.
TABLE-US-00001 TABLE 1 Phosphate Sulfate Nitrate Adsorbed
Filtration (mg/L) (mg/L) (mg/L) phosphorus* time** (min.) Ex. 1
Sample 1 <1 19.7 19.8 >50 1 Ex. 2 Sample 2 <1 19.0 19.7
>50 1 Ex. 3 Sample 3 <1 18.9 19.8 >50 1 Ex. 4 Sample 4
<1 19.2 18.8 >50 1 Ex. 5 Sample 1 5.6 39.4 39.4 86 3 Ex. 6
Sample 2 9.2 38.8 39.5 77 3 Ex. 7 Sample 3 8.8 39.1 39.3 78 3 Ex. 8
Sample 4 12.4 37.7 38.7 69 3 Com. 1 Sample 5 15.4 11.2 17.0 12 1
Com. 2 Sample 5 35.1 31.2 36.1 12 3 Com. 3 Sample 6 7.7 39.8 39.6
81 45 Com. 4 Sample 7 36.0 33.1 37.2 10 19 *The amount of adsorbed
phosphorus in terms of milligram (mg) per gram (g) of the sample
**Time taken to complete the filtration for solid-liquid
separation
Table 1 shows the concentrations of residual ionic species in the
simulated wastewater after treated, the amount of phosphorus
adsorbed by each sample, and the time taken to complete the
filtration for solid-liquid separation in the water purification
treatment performed by use of each sample.
In any of Examples 1 to 4, the supernatant solution contained
residual phosphate ions in a concentration less than the detection
limit and accordingly the phosphate ions were almost completely
removed. Further, it was also found that ions other than the
phosphate ions remained so sufficiently that their concentrations
were scarcely changed. This means that only the phosphate ions were
selectively removed. Even in the case where the simulated
wastewater contained phosphate ions in a high concentration
(Examples 5 to 8), the same effect was confirmed. Moreover, it took
a short time to complete the filtration and hence no practical
problem was found in each Example.
On the other hand, however, in Comparative Examples, the
concentration of residual phosphate ions was decreased in some
degree but was still relatively high as compared with Examples.
Further, the concentration of other ions, particularly, the
concentration of sulfate ions was considerably lowered. It was also
found that the nitrate ions in Comparative Examples less remained
than those in Examples. Particularly in Comparative Example 3
(employing the sample 6), the concentration of residual phosphate
ions was decreased but floc was so formed that it took a very long
time to complete the filtration. Accordingly, this process was
found to involve practical difficulties.
* * * * *